The research planned is directed at establishing the structure and arrangement of three of the major collagen genes (alpha1(I), alpha 2, alpha1(II)) in the chicken and the human genome, and at gaining some insight in the way they are selectively expressed in some tissues and totally repressed in others. The structure of alpha1 and alpha2 collagen gene clones, isolated from J. Slightom's chicken and human DNA libraries, are being determined. Gene expression will be studied by examining the primary gene transcripts, their subsequent processing, and the levels of type I and type II procollagen messenger RNA in both the nucleus and cytoplasm in cultured chick chondrocyte before and after these cells have been switched from producing type II to producing type I collagen.